The centrosome is a small structure found near the nucleus of most animal cells. Its main job is to organize microtubules, one of the three major types of protein filaments that make up the cell’s internal framework, or cytoskeleton.
Centrosomes are especially important when a cell divides. They help organize the microtubules that separate duplicated chromosomes into the two new cells. They also contribute to the organization of microtubules in nondividing cells, helping cells maintain their shape, position internal structures, and transport materials.
A centrosome is therefore best understood as a microtubule-organizing center rather than as a structure with a single function.
What is a centrosome made of?
A typical animal-cell centrosome consists of two cylindrical structures called centrioles, surrounded by a protein-rich material called the pericentriolar material, or PCM.
The two centrioles are usually positioned roughly at right angles to one another. Each centriole is built from microtubule structures arranged in a characteristic cylinder. The centrioles themselves are not the main site where microtubules are produced. Instead, proteins in the surrounding pericentriolar material provide the machinery that nucleates, or initiates, microtubule formation.
One of the most important components of this machinery is a protein complex called gamma-tubulin ring complex (γ-TuRC). It helps create a starting point from which microtubules can grow.
The centrosome’s organization changes during the cell cycle. Before cell division, the centrosome duplicates so that the resulting cell has two centrosomes. These two centrosomes move apart and help establish the two ends, or poles, of the mitotic spindle.
What does the centrosome do?
The centrosome’s central function is to organize microtubules. Microtubules are dynamic, tube-shaped filaments made primarily from the proteins α-tubulin and β-tubulin. They can rapidly grow and shrink, allowing cells to reorganize their internal architecture as conditions change.
Centrosomes help control where microtubules form and how they are arranged. In many animal cells, microtubules extend outward from the centrosome, creating an organized network throughout the cell.
This organization supports several cellular processes.
It helps organize the cell’s internal structure
Microtubules act as tracks along which molecular motors move cargo. Proteins such as kinesins and dyneins transport vesicles, protein complexes, and other cellular materials along these tracks.
By organizing the microtubule network, the centrosome helps establish the spatial arrangement of these tracks. This is particularly important in cells that need a strongly polarized internal organization.
The centrosome can also influence the position and organization of structures such as the Golgi apparatus, although cells can use other microtubule-organizing centers as well.
It plays a crucial role in cell division
The centrosome becomes especially important during mitosis, the stage of the cell cycle in which a cell separates its duplicated chromosomes.
Before mitosis, the centrosome duplicates. The two centrosomes then separate and establish opposite sides of the dividing cell. Microtubules grow between and around these centrosomes to form the mitotic spindle.
Some spindle microtubules attach, directly or through specialized protein structures, to chromosomes at regions called kinetochores. Others interact with microtubules extending from the opposite spindle pole or with structures near the cell cortex.
The resulting spindle provides the machinery needed to segregate duplicated chromosomes accurately. Each daughter cell can then receive a complete set of chromosomes.
Centrosome abnormalities can interfere with this process. For example, abnormal centrosome numbers can contribute to faulty spindle organization and chromosome-segregation errors, phenomena frequently associated with cancer cells.
It helps establish cell polarity
Many cells have distinct “front” and “back” or “top” and “bottom” regions, a property known as cell polarity. The organization of microtubules can help establish and maintain this directional arrangement.
In some cells, the centrosome serves as an important organizing site for the microtubule network that supports polarity. Its exact role varies considerably among cell types, however, and some polarized cells rely on additional or alternative microtubule-organizing centers.
How does the centrosome organize microtubules?
Microtubules are made from tubulin subunits that assemble into long filaments. Their growth is not random. Cells need proteins that can initiate microtubule formation and organize the resulting filaments.
The pericentriolar material surrounding the centrioles contains proteins that perform this organizing role. Among them, γ-tubulin-containing complexes provide templates that help nucleate new microtubules.
Once a microtubule has been nucleated, it can extend outward from the centrosome. Its two ends behave differently: one end, called the minus end, is generally associated with the centrosome, while the plus end tends to extend into the cell and undergoes particularly dynamic growth and shrinkage.
This arrangement gives the cell a directional microtubule network. Molecular motors and other proteins can then use the network for transport and structural organization.
The centrosome is not simply a permanent anchor for every microtubule, though. Microtubules are constantly reorganized, and cells can create organized microtubule arrays away from the centrosome when specialized functions require them.
What happens to the centrosome during the cell cycle?
Centrosome duplication is closely coordinated with the cell cycle so that, under normal circumstances, a cell produces the appropriate number of centrosomes for division.
A centrosome begins duplicating around the time the cell enters S phase, when the cell’s DNA is replicated. Each original centriole gives rise to a new daughter centriole positioned nearby. The two centrosomes eventually mature and separate as the cell approaches mitosis.
During mitosis, the two centrosomes become the primary spindle poles. After chromosomes have been separated and the cell completes division, each daughter cell inherits a centrosome containing a pair of centrioles at different stages of maturity.
This coordination matters because both too few and too many centrosomes can disrupt the normal organization of the mitotic spindle.
Are centrioles and centrosomes the same thing?
No. The terms are related but describe different structures.
A centriole is one of the cylindrical structures found within a typical animal-cell centrosome. A centrosome consists of a pair of centrioles together with the surrounding pericentriolar material.
The distinction is important because centrioles have functions beyond their role in the centrosome. In many cells, a centriole can become a basal body, a structure that organizes the formation of a cilium or flagellum.
The centrosome itself is therefore more than a pair of centrioles. Much of its ability to organize microtubules comes from the protein-rich material surrounding them.
What is the relationship between centrosomes and cilia?
Centrosomes are closely connected to cilia, hair-like projections found on the surfaces of many cells.
A centriole can migrate to the cell surface and become a basal body. The basal body then organizes the microtubule-based structure, called the axoneme, that forms the internal framework of a cilium.
Cilia can have different roles. Some move fluid or particles across a cell surface, while others act primarily as sensory structures that detect signals from the cell’s environment.
This means that centrioles participate in both centrosome function and the formation of specialized structures at the cell surface. The centrosome and basal body are related organizational structures, but they perform distinct roles in different cellular locations.
Do all cells have centrosomes?
No. Centrosomes are characteristic of animal cells, but not all eukaryotic cells use centrosomes as their primary microtubule-organizing centers.
Most higher plants, for example, lack the conventional centrosomes found in animal cells. They still have extensive microtubule networks and can organize microtubules effectively, but they do so using other structures and mechanisms.
Some animal cells can also organize microtubules without relying exclusively on the centrosome. This is especially important in differentiated cells whose microtubule networks have specialized arrangements.
The centrosome is therefore important, but it is not the only way a eukaryotic cell can organize microtubules.
Why are centrosomes important in human health?
Because centrosomes help organize the machinery of cell division, defects in centrosome number, structure, or function can have significant consequences.
A cell with abnormal centrosome duplication can acquire extra centrosomes. Multiple spindle poles can then form during mitosis, increasing the risk of abnormal chromosome segregation. Cells can sometimes cluster extra centrosomes together and still divide, but the underlying instability can contribute to abnormal chromosome distribution.
Centrosome abnormalities are common in many cancers, although their relationship with cancer is complex. They can be a consequence of cancer-associated changes as well as a potential contributor to genomic instability.
Centrosome-related defects can also affect cilia because centrioles serve as basal bodies. Since cilia are involved in movement, sensing, and signaling, problems with centriole or cilium formation can disrupt a wide range of cellular functions.
Why the centrosome matters
The centrosome is a compact cellular structure with an outsized role in organization. By controlling the formation and arrangement of microtubules, it helps cells build an orderly internal architecture, transport materials, establish polarity, and divide their chromosomes accurately.
Its most familiar role is as a microtubule-organizing center during cell division, where duplicated centrosomes help establish the mitotic spindle. But its functions extend beyond mitosis: centrioles can also give rise to basal bodies, linking centrosome biology to the formation and function of cilia.
Understanding the centrosome therefore means understanding one part of a larger cellular system in which microtubules, centrioles, molecular motors, and regulatory proteins work together to organize the cell in space and time.
